Conventional thermoplastic polymer compositions have a near limitless number of uses. As a result of having both durability and processability, thermoplastic polymers are used pervasively in various fields such as, for example, the automobile industry, manufacturing of industrial and domestic appliances, and hand-held utensils and tools.
Thermoplastic elastomer compositions are one type of thermoplastic polymer composition having a combination of both thermoplastic and elastic properties. These properties are generally obtained by combining a thermoplastic polymer with a rubber composition in a way such that the rubber is dispersed within a continuous phase of the thermoplastic polymer. Unlike conventional vulcanized rubbers, thermoplastic elastomer compositions can be processed and recycled like thermoplastic materials. Conventional thermoplastic elastomer compositions include, for example, polybutadiene or polyisoprene dispersed in a matrix of thermoplastic polymer such as polypropylene.
Thermoplastic polymer compositions, including polypropylene-based thermoplastic elastomer compositions, often suffer from long cycle times in thermoforming applications. The cycle time of a particular manufacturing process is a function of many factors, including factors derived solely from intrinsic properties of thermoplastic polymer compositions, such as for example melting temperature and crystallization temperature. Thermoplastic polymers having low crystallization rates and/or low crystallization temperatures require more time to cool and solidify so that a thermoformed article can be ejected from a die without losing shape. Long cycle times lead to inefficiencies in thermoforming processes, increased costs, and decreased productivity.
To shorten cycle time limitations, it is known to alter the crystallization kinetics of conventional thermoplastic materials, particularly propylene-based thermoplastic materials, by utilizing nucleating agents. In thermoforming processes, nucleating agents reduce cycle times by hastening crystallization. Unfortunately, nucleation agents are known to provide little or no effect on certain thermoplastic polymer compositions, such as for example thermoplastic elastomer compositions, especially when preparing commercial quantities. Nucleating agents may also interfere with curing elastomeric components. Lastly, utilizing nucleating agents often results in unwanted weight gain in thermoplastic elastomer compositions. Thus, industries that prepare thermoplastic elastomer compositions may abstain from using nucleating agents to reduce thermoforming cycle time. These same industries are searching for compositions that may be processed using shorter cycle times and exhibit a high service temperature while maintaining favorable elastomeric properties.
Accordingly there exists a current and long felt need for thermoplastic polymers that overcome known deficiencies in conventional compositions, have advantageous processing and thermoforming processing characteristics, and are generally suitable for thermoplastic elastomer (TPE) and thermoplastic vulcanizate (TPV) applications.